The Multiple module (or “mult”) is used to split signals so you can patch them to multiple places. Multiples are a vital part of any modular system, becuase you’ll want to send an output to multiple inputs quite often. There are two main types of multiples: passive and buffered. Both have their pros and cons.
The passive mult is one of the simplest modules concievable, both physically and conceptually. It’s made up of simply a series of jacks wired together. If you patch a signal into one jack, you can use any of the other jacks to patch that same signal elsewhere, letting you split one output and send it to multiple inputs. When signals are split this way, the voltage of each output will drop slightly as the signal is split. For most CVs or audio signals this is usually acceptable, but for precise CVs (like a V/Oct CV) this drop will be an issue. This issue is solved with a buffered mult.
A passive mult is less versatile but cheaper and easier to build than a buffered mult.
The Buffered Mult solves the above problem by buffering each output so there is no voltage drop. This means you can patch precise signals like a V/Oct CV to multiple places without any voltage drop. The tradeoff is that a buffered mult is more complicated, requiring a power connection and op-amps. A buffered mult is generally more versatile than a passive mult, but it’s more expensive and labor-intensive to build.
With a passive mult, you can plug the input into any jack and get the output from any jack, since it’s just a few jacks wired together. But with a buffered mult, due to the required electronics, there is a single designated input and multiple designated outputs.